Breakthrough could double wireless capacity with no new towers

September 6, 2011

Rice University graduate student Melissa Duarte with a "full-duplex" test device. The technology, which allows wireless devices to "talk" and "listen" to networks on the same frequency, could double throughput on wireless phone networks. Credit: Jeff Fitlow/Rice University

The days of waiting for smartphones to upload video may be numbered. Rice University engineering researchers have made a breakthrough that could allow wireless phone companies to double throughput on their networks without adding a single cell tower.

Rice's new "full-duplex" technology allows wireless devices like cell phones and electronic tablets to both "talk" and "listen" to wireless cell towers on the same frequency -- something that requires two frequencies today.

"Our solution requires minimal new hardware, both for mobile devices and for networks, which is why we've attracted the attention of just about every wireless company in the world," said Ashutosh Sabharwal, professor of electrical and computer engineering at Rice. "The bigger change will be developing new wireless standards for full-duplex. I expect people may start seeing this when carriers upgrade to 4.5G or 5G networks in just a few years."

In 2010, Sabharwal and Rice colleagues Melissa Duarte and Chris Dick published the first paper showing that full-duplex was possible . That set off a worldwide race to demonstrate that the technology could actually be used in a real network. This summer, Sabharwal and Rice's Achaleshwar Sahai and Gaurav Patel set new performance records with a real-time demo of the technology that produced signal quality at least 10 times better than any previously published result.

"We showed that our approach could support higher throughput and better link reliability than anything else that's been demonstrated, which is a plus for wireless carriers," Sabharwal said. "On the device side, we've shown that we can add full duplex as an additional mode on existing hardware. Device makers love this because real estate inside mobile devices is at a premium, and it means they don't have to add new hardware that only supports full duplex."

To explain why full-duplex wireless was long thought impossible for wireless networks, Sabharwal uses the analogy of two people standing far apart inside an otherwise empty arena. If each shouts to the other at the same time, neither can hear what the other is saying. The easy solution is to have only one person speak at a time, and that's what happens on two-way radios where only one person may speak at a given time. Cell phones achieve two-way communications by using two different frequencies to send and listen.

Rice's team overcame the full-duplex hurdle by employing an extra antenna and some computing tricks. In the shouting analogy, the result is that the shouter cannot hear himself, and therefore hears the only other sound in the arena -- the person shouting from far away.

"We send two signals such that they cancel each other at the receiving antenna -- the device ears," Sabharwal said. "The canceling effect is purely local, so the other node can still hear what we're sending."

He said the cancellation idea is relatively simple in theory and had been proposed some time ago. But no one had figured a way to implement the idea at low cost and without requiring complex new radio hardware.

"We repurposed antenna technology called MIMO, which are common in today's devices," Sabharwal said. "MIMO stands for 'multiple-input multiple-output' and it uses several antennas to improve overall performance. We took advantage of the multiple antennas for our full-duplex scheme, which is the main reason why all wireless carriers are very comfortable with our technology."

Sabharwal said Rice is planning to roll its full-duplex innovations into its "wireless open-access research platform," or WARP. WARP is a collection of programmable processors, transmitters and other gadgets that make it possible for wireless researchers to test new ideas without building new hardware for each test. Sabharwal said adding full-duplex to WARP will allow other researchers to start innovating on top of Rice's breakthrough.

"There are groups that are already using WARP and our open-source software to compete with us," he said. "This is great because our vision for the WARP project is to enable never-before-possible research and to allow anyone to innovate freely with minimal startup effort."

Sabharwal's team has gone one step further and achieved asynchronous full-duplex too  that is one wireless node can start receiving a signal while it's in the midst of transmitting. Asynchronous transmission is import for carriers wishing to maximize traffic on their networks, and Rice's team is the first to demonstrate the technology.

"We've also developed a preliminary theory that explains why our system is working the way that it is," Sabharwal said. "That's also important for carriers and device makers, because engineers aren't likely to implement something like this without a clear understanding of fundamental tradeoffs."

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Full-duplex was the predecessor to MIMO. All these guys did was rediscover old technology.

The idea of full-duplex preceded MIMO, yes. But MIMO was easy to implement, and no one figured out how to do Full-Duplex. It's not a technology if no one can do it. The Star Trek Warp Drive isn't a technology, its a fantasy -- and so was Full-duplex until now.

They still run the limitation of the circuit to the towers, but less hardware to install for upgrades. But may be very useful for bridging towers where physical lines cannot be run. But I doubt this will help the end user in any way except perhaps battery power. Not to mention we will still have bandwidth caps on so called "unlimited" data plans.

Wireless providers are milking data costs for all it's worth. Telstra (A backwards Australian provider) was charging data by the kilobyte a couple years ago. They are still a rip-off now.

I have a new provider now that gives me 4GB/Month data with unlimited sms/calls for $40/month within the country. I think prices will only get better. Internet is only getting faster and cheaper! It just takes time.

When it comes right down to it everything is just data. It really is dirt cheap once the infrastructure is in place.

If anything is clear, it's the cynicism we all appear to share about our "job creators" in the private sector. Don't get me wrong, I find it a justifiable position. It's likely that the "minimal new hardware" claim will be exaggerated or be hyperbolized in a way to warrant an increase in cost that far outweighs its true cost, but then again, this is capitalism we're talking about, and corporations owe allegiance to no one.

Yes, full duplex can mean more speed, because channels previously reserved for uplink can then be used for downlink too. Simple example, let's assume we have frequencies named 1,2,3 & 4 available. Previously 1 & 2 were for downlink and 3 & 4 for uplink. With full duplex 1-4 can be used for downlink and 1-4 also for uplink. So we just doubled the channels available for downlink (and for uplink too).

Full duplex is used widely in telephone calls. That is, plain old telephone calls. Dial-up was the last consumer-level service that actually used full duplex, as it used different frequencies to transmit and receive the data.Like PPihkala said, there's seperate uplink and downlink frequencies, but when it comes to radio, the same antennae cannot send and receive at the same time. As the article stated, they had to add an antennae in order to apply their scheme.Now, here's the downside... the phone will essentially be emitting a good deal more RF energy travelling through the tissues in your hand and forearm, into your hip when in a belt holster, and into your head when holding it to your ear.Honestly, that's one reason I don't use AT&T... when I'm on a call and holding the phone to my ear, my phone's ONLY putting out the power for the voice call, and NOT for data. And, data is the service that causes most of the RF emissions.

How does a dual radio (two antennae) have to put out more RF just to achieve this? It's just simultaneous xmt/rcv in close proximity with hardware and software to work around the interference problem. I don't see how they need more gain for this. Wouldn't more gain make it HARDER on this?

Also, once you start using 4G, you won't have a choice in carriers that doesn't xmt data during a call.

Dial-up was the last consumer-level service that actually used full duplex, as it used different frequencies to transmit and receive the data.

- Ricochet

Dial-Up through POTS for both voice and data used a transformer configuration known as a hybrid for Full Duplex over a 2 wire system, essentially just an anti phase cancelling arrangement.

Digital signal processing and various multiplexing techniques are quite capable of full duplex in mobile phones.

.. but when it comes to radio, the same antennae cannot send and receive at the same time.

A single antenna can be used for transmit and receive by using adequate carrier frequency separation and signal flow control.

I suppose for the pedantic, high speed switching of half duplex is only pseudo full duplex, even though the result is identical with the exception that throughput is limited by the available bandwidth.

... with the exception that throughput is limited by the available bandwidth.

That's just it, isn't it? spectrum = bandwidth = throughput (well, not 1:1, but you get the point) As I'm sure you realize, these guys didn't care about creating "real" full duplex, just to say they did it; they've managed to come up with more throughput potential with less hardware (second radio). Very cool, imo.

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